Conventional removable core cylinders are removable from a lock housing under the control of a control key for removing and e.g., replacing, the core. An operating key, or master key, is used to operate the lock in its normal condition and does not affect the removability of the core. Conventional removable cores utilize conventional pin tumblers which are evenly spaced in a single row along the length of the key barrel, which make removable cores subject to "picking" and thus, limiting the security they can afford. Conventional removable core cylinders are also more subject to security violations with unauthorized duplicated control keys.
Key-removable, interchangeable cores permit unskilled persons to rekey locks (i.e., block-out existing locks) without opening the door or removing the lock from the door. The cylinder is removed from the lock housing through the use of a control key, and a different interchangeable core cylinder of the same manufacturer can then be inserted into the lock housing, whereby the user can quickly and easily change a lock or locks without calling a locksmith.
Interchangeable cores are pinned for release from their housings by a single control key. The control key is actually a "top" master key whose sole function is limited to operation of the locking tab which retains the core in the lock housing. Interchangeable core control keys are not visually distinguishable from other keys in the system. Typically, the core is also pinned to one or more master keys and to a tenant key. Such a system usually requires three or four pin segments in each pin column; an arrangement which offers very limited pick-resistance.
Key-removable, interchangeable cores are manufactured by most American lockmakers. However, core interchangeability is usually limited to the housings of a single manufacturer.
High security locks include at least two mutually independent lock systems and are manipulated by different codes on one and the same key. The blade of the key to the system lock has a first, conventional code which coacts with the pin tumblers in the cylinder.
One of the high security features is the use of an independent locking mechanism on the side of the key--a sidebar--which is mounted in the radially outer part of the plug and which coacts with a row of side tumblers positioned laterally in the cylinder plug. The side bar prevents the cylinder from operating, should the top pins be "picked". The side bar also provides the system owner with an exclusive key that is controlled by the factory.
The side tumblers in the sidebar are manipulated by a code provided on a side-part of the key, which when the key is inserted into the lock, engages a region of the side tumblers. When the correct key is inserted, the first-mentioned tumblers form a dividing plane between the cylinder plug and the cylinder shell and the side tumblers are moved to positions in which a radially and inwardly directed control part on the sidebar is enabled to engage waisted portions on the tumblers, such that the sidebar will move into the plug against the action of a spring force as the plug is rotated by means of the key.
Examples of sidebars used in conventional removable core cylinder assemblies, are disclosed in Widen (U.S. Pat. No. 4,356,713), Cox (U.S. Pat. No. 5,209,087), and Oliver (U.S. Pat. No. 3,298,211, Re. 31,910).
Although no standardization exists with respect to all manufacturers of removable cores, there have been some improvements in the prior art with respect to standardization of face plates which cover one end of the cylinder shells, such as that described in Best (U.S. Pat. No. 1,575,092).
Removable core cylinders with locking tabs (locking or control sleeves) having the same number of pin chambers as the cylinder shell and cylinder plug, and having a face plate permanently assembled to the front of the cylinder shell, and manufactured by Arrow, Best, Falcon, KSP, Medeco, and others, have been standardized. This subset of removable cores is called interchangeable cores. The majority of lock manufacturers make interchangeable core locks which accept interchangeable core cylinders of different manufacturers.
As an example of the prior art standardized interchangeable core cylinder assemblies, FIG. 1 discloses a figure 8-shaped outer cylinder shell 1, permanently assembled with a face plate 12 to cover the axial recess provided for the locking tab 3 and to create a bearing surface for the head of the cylinder plug 4, a control sleeve 2 having the locking tab 3 formed thereon fitted in the cylinder shell and which also serves as a housing for the cylinder plug 4, a rotatable key barrel or plug 4 which is fitted in the sleeve 2, and a key stop disc or retainer 5, which is similar to that described in Sussina (U.S. Pat. No. 5,176,015, Re. 35,518), and also Russell et al (U.S. Pat. No. 3,298,211), and Juang (U.S. Pat. No. 5,507,163). The control key 6 has a stop 13 and cannot be withdrawn from the core unless the locking tab 3 is in the extended (locking) position. The pin stacks 7 in the removable core cylinder lock assembly 8 include bottom pins 9 which are radially adjusted within the bores 10 by corresponding bittings 11 cut in the top edge of the key 6.
As can be seen from the prior art in FIG. 1, the locking tab 3 is integrally formed with the control sleeve 2, which means that the outer cylinder shell 1, in order to provide for the sleeve 2, has thin walls that are subject to deformation.
Further, another problem in the prior art is that, although the sidebar concept is used in removable core cylinder locks to provide greater security, standardized interchangeable cores have no room for the sidebars--thus limiting the convenience of using an interchangeable core.
Further, permanent assembly of the cylinder shell and the face plate, thin walls of the cylinder shell and ultra thin walls of the control sleeve forces the manufacturers to sell interchangeable cores only as one complete assembly. This leads to duplication in inventory based on finish and keyway, which add to distributors inventory costs.
Accordingly, there is no existing interchangeable core cylinder which has modular parts which can be purchased separately and the core built to an end-user's needs, wherein the modular elements are independently sturdy, and wherein the interchangeable core can provide the greater security of a sidebar feature.